DE60023270T2 - Method and apparatus for controlling the absorption of a liquid sample through an absorbent layer - Google Patents

Abstract

A method and apparatus for controlling the absorption of a liquid sample through an absorbent layer (2) and reducing the effect of hematocrit by applying the sample on one side of the layer (2a) and providing an air gap (4c) on the opposite side, so that absorption is controlled by preventing the release of air from the air gap.

Description

background the invention

Field of the invention

The The present invention relates to liquid samples to be analyzed and more particularly to controlling the absorption of a liquid sample through an absorbent layer, reducing the effect of hematocrit is reduced.

Background information

test strips are widely available, for convenient liquid samples analyze. Such a test strip typically exists one or more layers of absorbent material, which contains chemical reagents. Meets a fluid sample on the absorption layers, the reagents react with the corresponding ones Components in the test sample. To determine the components of the sample, The measurement of the ensuing response to many different types are performed.

For certain Diabetes patients are e.g. useful, monitor the glucose concentration in their blood. A glucose test strip may have an absorbent layer containing reagents which react with the glucose in the blood sample. When a Patient gives a blood sample on the absorbent layer, so reacts the reagent with the glucose in the sample. If the reaction to a measurable color change leads (what the absorbent layer e.g. changed from colorless to dark blue), then the reaction can be measured and the amount of produced Color is related to the glucose concentration in the blood sample.

One Patient typically gets the test strip with a separate Use device, which measures the chemical reaction in the absorption layer and the Indicates glucose concentration of the patient. Such a device used a reflection meter, which Measures the reflected light of specific wavelengths to capture the light that from the surface the absorption layer is reflected. Because the chemical reaction causes a color change in the absorption layer, the reflection meter, the reaction by Detection of changes of the light which reflects from the surface of the absorption layer becomes. For example, Can the reflectance meter when the chemical reaction progresses, an increase of the reflected by the absorption layer blue light. The reflection of light can thus be used to monitor the chemical reaction and thus the glucose concentration in the blood sample.

The Reflection measurements can however, they are subject to fluctuations that lead to inconsistent results to lead. One factor is the volume of the liquid sample that is on the Absorption layer is given. When the sample is on the absorption layer Ideally, the sample should ideally be completely removed from the layer are absorbed. In practice, however, it may be that an excess of sample is applied, so that the Absorption layer over with the sample is saturated becomes. As a result, a layer of excess sample may be on the bottom surface of the absorption layer, causing the surface to be shiny. This shine, called wet-through, can dramatically alter the reflection of the absorption layer increase, the measurement of the reaction distort and the patient misleading information deliver.

A second size, the The test results may affect the hematocrit of the patient's blood a measure of the rela tive Amount of red blood cells and plasma in the blood sample is. As the hematocrit of the blood sample of a Patients may vary, may also be the absorption of the sample through the absorption layer vary, leading to hematocrit-dependent measurements of glucose concentration of the patient's blood.

Therefore It is necessary to absorb the absorption of a liquid sample by an absorbent Layer control and reduce the hematocrit effect. The present invention fulfills these requirements and also offers associated benefits.

Summary the invention

The present invention provides a method for the controlled absorption of a liquid sample through an absorbent layer 2 by (a) an air gap 4c passing through the absorption layer 2 , at least one sidewall 4d and a translucent window 6 is defined; and (b) adding the liquid sample to the absorbent layer on the air gap 2a opposite side. As a result, the absorption of the sample is controlled by the escape of air from the air gap 4c is avoided.

The present invention also provides a system for carrying out the method of the invention. The system has an absorption layer 2 , at least one sidewall 4d and a translucent window 6 , where layer, wall and window the air gap 4c define.

Short description the drawings

1 Figure 4 is an isometric view of an embodiment of the system (not to scale).

2 is a section through an embodiment of the system (not to scale). The cutting plane is in 1 specified.

3 Figure 13 is an exploded isometric view of another embodiment of the system, including optional components (not to scale).

The clarity half are the associated Number of components and characteristics listed below:

1

Second Layer (optional)

2

Absorption layer, with application area 2a and opposite the viewing area 2 B ,

3

Adhesion layer with hole 3c and inner surface 3d

4

Handle with hole 4c and inner surface 4d

5

Adhesion layer with hole 5c and inner surface 5d

6

translucent window with surface 6a ,

7

general line of sight

4 shows a comparison of the relative volume dependence of the test tire model A (with air gap) and model B (without air gap).

5 shows a comparison of the relative hematocrit dependency of the test strips Model A and B.

detailed Description of the invention

The present invention provides a method and system for controlling the absorption of a fluid sample through an absorbent layer. If a liquid sample on the application area 2a the absorption layer 2 given, the sample is absorbed. As in the embodiment in 2 shown is an air gap 4c provided by the viewing area 2 B on the opposite side of the absorbent layer 2 , at least one sidewall 4d and the surface of a translucent window 6a is defined. The defined "air gap" is an airtight chamber with ambient air pressure.

The Absorption of the liquid sample causes a slight increase compared to the ambient air pressure the pressure within the air gap. This pressure increase can by the decrease in the effective volume of the air gap can be explained because the liquid, which is absorbed by the layer, the air within the layer repressed. Because the air gap no way for the displaced Air has to escape, the air gap effectively prevents absorption further sample through the absorption layer before.

Due to the air gap, no excess sample is absorbed by the absorption layer, but it may be on the application surface 2a collect or through an optional second layer 1 be absorbed. Otherwise, a layer of excess sample on the viewing surface of the absorption layer 2 B cause an undesirable result, which is called wet-through. Thus, the absorption of excess liquid sample is controlled by the given air gap.

"Liquid samples" which may be used with the invention include any liquid containing an analyte to be measured, eg blood, serum or plasma "Human bodily fluids" such as sweat, tears, saliva, sperm, cerebrospinal fluid, sputum, urine, cervical mucus or smears, but also includes food, environmental or industrial samples, depending on the required application of the article Prerequisite that it is liquid and contains an analyte for measurement.

The fluid sample may be assayed for specific "analytes of interest" which may be any substance to be detected and quantified in terms of their concentration, for example, glucose, fructose or other sugars, or cholesterol, ketones, lipids, uric acid or specific amino acids, eg phenylalanine The analyte may also consist of proteins, eg amylase, creatine kinase or alanine aminotransferase Furthermore, glycosylated proteins may also be used, eg glycosylated serum or plasma proteins, measurable by fructosamine, or glycated red blood cell protein, which is measured glycated hemoglobin, specifically glycohemoglobin Hb _A1C . Other analytes are described in US Patent No. 5,597,532.

The "absorption layer" can be made of any Material that is permeable to gas in the dry state and for liquids absorptionsfähig is, however, relatively less permeable to gas in whole or in part with liquid saturated Status. A special absorption layer is BIODYNE A, a nylon membrane with 0.65 μm Pore size (Pall Corp .; East Hills, New York). The absorption layer may be a reagent which indicates the presence of an analyte, e.g. glucose or fructosamine. Typical absorption layers are disclosed in U.S. Pat. patent No. 5,470,752, U.S. Pat. U.S. Pat. No. 5,597,532 and U.S. Pat. Patent No. 5,695,949.

A especially useful Contains absorption layer a reagent that reacts with glucose in the fluid sample, e.g. a glucose oxidase / horseradish peroxidase system (Toyboyo Inc., Tokyo, Japan). Another useful System for reacting with glucose is N-ethyl-N-2-hydroxy-3-sulfopropyl-3,5-dimethylaniline (MAOS) (Dojindo Laboratories, Kumamoto, Japan) and N-ethyl-N- (2-hydroxy-3-sulfopropyl) -m-toluidine (TOOS). Close other reagents the combination of 4-aminoantipyrene and chromotropic acid (AAP-CTA) and the combination of 3-methyl-2-benzothiazoline hydrazone hydrochloride (MBTH) and either 3-dimethylaminobenzenes (DMAB) or 8-anilo-1-naphthalenesulfonate (ANS).

The absorption layer can be on a handle 4 be applied so that the user can hold the test strip without touching the absorption layer. The handle contains a hole 4c , whose interior walls 4d partially define the air gap. Eg shows 3 that the side wall 4d the inner surface of the hole 4c is. Even if the hole 4c in 3 is shown circular it may have any shape, so that there may be two or more specific side walls that form the air gap.

The handle 4 can on the absorption layer 2 be applied with all means of adhesion of two layers, as long as the resulting air gap is secured against air leakage and he the viewing surface of the absorption layer 2 B along the line of sight 7 does not cover. The adhesives may be, for example, acrylic, silicone or rubber based. A particularly useful acrylic-based adhesive layer is FAS-TAPE 8311, a double-coated acrylic-based adhesive (Avery-Dennison, Inc., Pasadena, California). Other adhesives include 3M 444 or 3M 415 double coated adhesives (3M, Minneapolis, Minnesota). Means for attaching the sintered polymer to a solid also include PVC plastic adhesive, epoxy resin, hot stamping, clamping, screwing, nailing, compression matching, and vacuum immobilization.

The test strip also has a translucent window 6 , which through one of its side walls partially the air gap 4c Are defined. The "translucent window" should allow the light, essentially along the line of sight 7 walk along to the window 6 on the viewing area 2 B from where it passes through the window 6 is reflected through, so that the reflected light is detectable.

Because the fluid sample is warmer or colder than the ambient temperature at the surface of the window 6 It can be along the viewing line 7 come to interference. Accordingly, the window must have been treated to be "non-opacifying" so that the temperature differences in the window do not precipitate in the form of moisture condensation by the ambient environment 6 can be applied to any of the above-described ways of adhering two layers to the handle 4 be attached.

In this way, as in 3 can show an adhesion layer 3 be used to the Ab sorption 2 to the handle 4 and another adhesion layer 5 to the handle 4 at the window 6 to fix. In such cases, the adhesive layers should 3 and 5 holes 3c and 5c have to not disturb in the line of sight. The air gap is then in turn through the viewing surface of the absorption layer 2 B , through the inner sidewalls of the adhesive layer 3d , the handle 4d and the second adhesion layer 5d and through the window surface 6a Are defined.

Additional layers can be added to the system, eg a second layer 1 for separating a complete blood sample so that the blood plasma is the application surface of the absorption layer 2a reached. Such layers are prior art and exemplified in US Pat. No. 5,725,744.

Examples

I. Construction of a Test tire with air gap

To compare the design of the test strips with and without the particular feature of the air gap, three test strip models have been assembled: Model A with and Model B and C with no air gap. Each of the models had a solid polyester grip 4 and an absorption layer 2 consisting of a 0.65 μm pore size BIODYNE A nylon membrane (Pall Corp., East Hills, New York). The absorption layer was coated with a glucose oxidase / horseradish peroxidase system (Toyboyo Inc, Tokyo, Japan) and MAOS (N-ethyl-N-2-hydroxy-3-sulfopropyl-3,5-dimethylaniline, sodium salt, monohydrate) (Dojindo Laboratories; Kumamoto , Japan). The handle 4 and the absorption layer 2 were at the adhesion layer 3 made of FAS-TAPE 8311, a double-coated acrylic-based adhesive (Avery-Dennison, Inc., Pasadena, California). These common features were modified as follows in the three models.

Model A, with the characteristic air gap, also had a translucent window 6 consisting of MYLAR D, a 4 mm thick transparent polyester film (Dupont & Co., Wilmington, Delaware). The film was dipped in PERFECT-VIEW, a non-aerosol anti-fog lens cleaner (Tyr Sport Inc, Huntington Beach, California). The film was made with the help of an adhesive layer 5 to the handle 4 attached, which consisted of the same material as the adhesive layer 3 (so). A second layer 1 consisted of T667 or 6664, a white polyester spunbond (Reemay, Inc., Old Hickory, Tennessee). The second layer was treated with 0.0001-0.1% PLURONIC polyoxypropylene-polyoxyethylene block copolymer (Pragmatics Inc, Oak Ridge, Tennessee), 8% mannitol, and 0.15% hexadimethrine, all in 0.85% NaCl -Solution.

Model B had a hydrophilic, 0.0635 cm thick second layer 1 POREX XM-1342 sintered high density polyethylene (HDPE) treated as above for the second layer 1 described in Model A. The layer was further treated as described in US Patent No. 6,024,919, filed January 14, 1998.

Model C had a second layer 1 consisting of T667 or 6664, a white polyester spunbonded web (Reemay, Inc., Old Hickory, Tennessee). This second layer has been treated as well as the second layer 1 in model A is described.

II. Preparation of test samples and measurement methods

Complete blood tests, with ethylenediaminetetraacetic acid (EDTA) treated as a anticoagulant, were prepared in such a way that the Samples can be converted to a value less than 50 mg / dl, to then fill with a concentrated glucose solution. The final concentration Glucose in the sample was analyzed using a YSI Stat-2300 glucose analyzer (Yellow Springs Instruments Inc., Yellow Springs, Ohio).

The sample was then placed on a test strip and inserted into a device containing a reflectance meter. A light-emitting diode (LED) in the apparatus irradiated 635 nm light toward the viewing surface of the absorption layer 2 B , essentially along the line of sight 7 , The reflection on the viewing surface 2 B was time-dependently measured by the reflectometer using a silicon photodiode which generates an analog signal. This signal is then further processed by a transconductance amplifier, a synchronous detector, an analog-to-digital converter and a microprocessor. The automatic processing and analysis of such detect signals are well known in the field of medical devices (see, eg, US Patent 5,597,532). Based on a standard curve generated using solutions of known glucose concentration, the microprocessor then displays the calculated values for glucose concentration.

III. Improvement of Consistency of measurements through the use of an air gap

The The following example shows that the Test strips with the feature air gap more consistent measurements produce as those without air gap.

blood samples with a hematocrit adjusted to 40% were at 5 different Glucose concentrations prepared: about 50, 100, 200, 350 and 500 mg / dl. The concentrations were later checked by the YSI Stat-2300 Glucose Analyzer. 15 μl samples were taken brought on every 16 strips of the three models and then measured by using the device described under Example II. The results were in terms of the percentage deviation coefficient (% CV = standard deviation / mean) as follows:

sDiese Results show that Model A (with the characteristic air gap) a significantly smaller deviation has as the models B and C (both without air gap), which ultimately leads to more consistent measurements.

IV. Reduced volume dependency through the use of the air gap

As As discussed above, it can happen that the measured glucose concentration due to the wet-through effect as a function of the sample volume, what was applied to the strip may vary. The following Example shows that the Measurements of test strips with an air gap are subject to less frequent fluctuations, which can be attributed to a fluctuating volume.

As in Example III. were blood samples at about 100, 300 and 500 mg / dl prepared. Samples of 3.5, 4, 5, 10, 15, 20, 30 and 40 μl were from each of these concentrations taken on 4 strips of models A and B and then measured, by using the device described in Example II.

The results are in 4 representing the average measured glucose concentration (y-axis), with model A (three solid curves) and model B (three dotted curves) at different sample volumes (x-axis) and different effective glucose concentrations (lower, middle, and upper) Pair of each solid and dotted lines) were used. It can be seen that the measured glucose concentrations for model A (with air gap) are more consistent over a range of 4-40 μl sample volume. In contrast, Model B measurements are consistent only in the 10-40 μl range.

hereby it is shown that it less likely is that with model A (with air gap) measured concentration by the sample volume affected is measured as the model B measured.

V. Improved hematocrit independence through the use of the air gap

The measurements of glucose concentration may also vary depending on the hematocrit, the one Ratio of the relative amount of red blood cells and plasma in a blood sample. The following example shows that the results obtained using air-gap test tires are less affected by the hematocrit of the blood sample than those obtained using non-air-gap test tires.

As in Example III. described, were blood samples with about 100, 200 and 400 mg / dl prepared, the one hematocrit of 0 (plasma), 20, 30, 40, 50, 60 and 80%. This represents 80% hematocrit a sample for Was centrifuged for 30 min at 5000 rpm and no longer contains plasma. One Sample volume of 15 μl each was applied to 8 strips of models A and B and it was the device used, which was described in Example II.

These results, see 5 showing the average measured glucose concentration (y-axis), with model A (three solid traces) and model B (three dotted traces) at different hematocrit values of the samples (x-axis) and different effective glucose concentrations (lower, middle, and lower) upper pair of each solid and dotted lines). It can be seen that Model A results in relatively consistent glucose measurements in the range of hematocrit values. In contrast, the model B may erroneously result in too low values as the hematocrit increases, especially if the sample contains a high concentration of glucose.

From this it can be seen that the Measurements in which the model A (that model with the feature Air gap) are less hematocrit-dependent than model B, which has no air gap.

Claims (7)

Method for controlling the absorption of a liquid Sample through an absorbent layer, with the steps (A) Providing an air gap through an absorbent layer, at least one sidewall and a translucent (translucent) Window is defined; and (b) applying a liquid sample on the absorbent layer on one side, which is the air gap opposite; in which the absorption of the sample is controlled by preventing the Release of air from the air gap. The method of claim 1, wherein the sample comprises a human body fluid is. The method of claim 2, wherein the liquid is a blood test. Device with an absorbent layer, at least a side wall and a translucent window, in which the Layer, the walls and the window define an air gap. Apparatus according to claim 4, wherein the window non-clouding. Apparatus according to claim 4, wherein the absorbent Layer contains a reagent, indicating the presence of an analyte. Apparatus according to claim 4, further comprising a second layer, which has contact with the absorbent layer.